Patent GB-1387406-A (GB)
Title: Feature selection in image analysis
IPC: G06F3/033
Filed: 1971-04-30
Abstract: 1387406 Image analysis IMAGE ANALYSING COMPUTERS Ltd 24 April 1972 [30 April 1971 26 Aug 1971] 12313/71 and 40008/71 Heading G1A In an image analyzis system, a particular feature 226, Fig. 8, on a CRT display, is selected by means of a light pen 224 so that video signals relating to the feature may be gated to a computer by 244, 246, where a measurement of a characteristic such as volume or area of the feature may be performed. The light pen circuit is shown in Fig. 2 in which 14 represents the light pen photo-diode, and junction 34 the video input which has been compared with a reference level and so relates only to features. On the detection of the CRT spot by the light pen, a pulse is produced which sets bistable 16 once per frame. This results in monostable 20 producing a short duration (picture point interval) pulse 22, Fig. 1. This may be delayed by four times its length,(pulse 26) Fig. 1 in 24 before application to OR-gate 28. The use of the loop including a delay 32 of one live-scan minus one picture point interval and the shift register 42, 44 and OR-gate 46, is to develop a gating pulse at 50 of three picture point intervals. This gating pulse is applied via OR-gate 52 to AND-gate 54, so that any part of a feature intersect pulse at 34 which is coincident with the gating pulse is released to 58 (see 63) Fig. 1. The portion 67 of the intersect pulse before the gating pulse is not transmitted.  To ensure that the rest of the intersect pulse, after the gating pulse has finished, is released, the loop containing AND-gate 60 is provided. Further, to ensure that the equivalent parts of intersect pulses in subsequent line scans are released, the signal at 58 is fed via 86 and AND- gate 92 to shift register 82 which has a delay of one line scan, and has a return loop to OR-gate 52 and AND-gate 54, via OR-gate 96. In order to provide a "look-ahead" facility as described with reference to Figs. 3-6 (not shown) and so ensure that intersect pulses encompassing the whole width of a feature, are released, outputs to OR-gate 96 are also provided from register units 72-78. However, this introduces the problem of intersect pulses from closely adjacent features being released Fig. 5 (not shown). To avoid this, the first part of the register 82 is divided up into four separate bistables 64-70, and associated circuitry 114-150 is provided.  A further modification of the circuit to follow an advance of a leading edge of a feature which is too sudden for the circuit of Fig. 2 alone to cope with, is described with reference to Fig. 7 (not shown). In the arrangement of Fig. 8, as shown, the computer 244 for calculating selected feature  volume operates on the amplified video signal directly. Computer 246 operates on the detected video signal i.e. feature intersect pulses, and calculates area. Switches pairs SIA, SIB and S2A, S2B are respectively ganged and closed by the light pen operator (they may be single switches on the light pen itself, Fig. 9 (not shown) or are floor or monitor-mounted) so that measurements relating to features all having a particular similar characteristic e.g. shape, colour, may be accumulated in accumulator pairs Al, B1 or A2 or B2. The video or detected signals and the light pen field of new may be displayed on the monitor and the selected feature brightened up. The light pen is rendered insensitive to ambient light variations by the phosphor being of a kind emitting visible and ultra-violet or infrared radiation, the light pen detector being rendered sensitive only to the ultra-violet or infrared e.g. by a filter. Other measurements besides area and volume may be horizontal and vertical projection and perimeter. The light pen store selection switching apparatus is described and claimed in Divisional Specification 1387407.